The present invention relates to a piezoelectric element. More particularly, the present invention relates to a piezoelectric portion which has very high piezoelectric properties, and which has a high rate of increase of displacement as an actuator in the case of applying a large electric field and a high decomposability as a sensor in the case that a great force is applied.
In recent years, piezoelectric elements have been used in ink jet printer heads, speakers, microphones, etc.
As the piezoelectric elements, there are generally known those comprising a ceramic substrate, a piezoelectric portion made of a piezoelectric ceramic composition, formed on the substrate, and electrodes electrically connected to the piezoelectric portion. As to the piezoelectric ceramic composition constituting the piezoelectric portion, various improved compositions have been disclosed.
For example, a Pb(Mg1/3Nb2/3)O3xe2x80x94PbTiO3xe2x80x94PbZrO3 ternary system solid solution composition and a piezoelectric ceramic composition wherein part of Pb in the above composition is replaced by Sr, La, etc., were disclosed [Japanese Patent Publication S44-17103, Japanese Patent Publication S45-8145]. With regard to a piezoelectric portion itself which are the most important factor determining the piezoelectric element properties of the piezoelectric element, a piezoelectric element having excellent piezoelectric properties (e.g. piezoelectric d constant is expected.
When a piezoelectric element is produced actually by superposing a piezoelectric material made of the above piezoelectric ceramic composition on a ceramic substrate and then subjecting the piezoelectric material to heat treatment, the obtained piezoelectric portion has a low density, and therefore, there have been pointed out such a problem that the piezoelectric element has a low flexural displacement or, when a voltage is applied thereto, it causes dielectric breakdown at the low density area. In particular, this problem is remarkable in the case of a piezoelectric element having a structure that a negative electrode and a positive electrode are disposed between piezoelectric portions alternatively, and its improvement has been strongly demanded.
In addition, sufficient piezoelectric properties cannot always be obtained with a piezoelectric portion made of the aforementioned piezoelectric ceramic composition, and there have been such a problem that when a voltage is raised to increase a flexural displacement, an increase of the flexural displacement obtained is very small relative to an increase of voltage on a side of a high electric field of 4 kV/mm or more.
Hence, there has been proposed a piezoelectric element produced by previously heat-treating a piezoelectric material made of the above piezoelectric ceramic composition to produce a piezoelectric portion, and then attaching this piezoelectric portion onto a ceramic substrate (Japanese Patent Application H11-29357).
In this piezoelectric element, attention was paid to a fact that use of a ceramic substrate impairs the densification of a piezoelectric portion. Thus, the piezoelectric element was accordingly improved in piezoelectric properties by means of obtaining a dense piezoelectric portion where a piezoelectric material made of a piezoelectric ceramic composition was previously heartbeat.
In this piezoelectric element, however, it is necessary to use an inorganic or organic adhesive at the time of attaching the piezoelectric onto the ceramic substrate. Therefore, there have been such problems that the adhesive impairs the vibration transmitability between the ceramic substrate and the piezoelectric or the adhesive components infiltrate into the piezoelectric or the ceramic substrate, deteriorating their properties.
In addition, in this piezoelectric element, no consideration is given to a piezoelectric ceramic composition itself constituting a piezoelectric portion. Therefore, there has been a problem that sufficient piezoelectric properties cannot always be obtained like the aforementioned piezoelectric element, and further, an increase of the flexural displacement obtained is very small relative to an increase of voltage in a region of a high electric field.
The present invention has been completed in view of the aforementioned problems and aims at providing a piezoelectric element which has very high piezoelectric properties, which is excellent in vibration transmittability between a substrate and a piezoelectric portion, and where linearity of a flexural displacement to voltage is ensured till a high electric region, and a method for production thereof.
Incidentally, in a piezoelectric element of the present invention, the aforementioned effect is great in a structure of laminating piezoelectric portions and electrodes alternatively to give a plurality of layers. The piezoelectric element can be suitably used for an actuator, a sensor, etc.
The present inventor made a study in order to solve the aforementioned problems. As a result, the present inventor found out that when there is used, as a piezoelectric material, a piezoelectric ceramic composition composed mainly of a PbMg1/3Nb2/3O3xe2x80x94PbZrO3xe2x80x94PbTiO3 ternary system solid solution composition of particular formulation and containing NiO in a particular proportion, the densified piezoelectric portion can be obtained even when a piezoelectric material is superposed on a substrate and then heat-treated, whereby the aforementioned problems can be solved. The present invention has been completed based on the above finding.
That is, according to the present invention, there is provided a piezoelectric element including a ceramic substrate, and piezoelectric portion made of a piezoelectric ceramic composition containing a PbMg1/3Nb2/3O3xe2x80x94PbZrO3xe2x80x94PbTiO3 ternary system solid solution composition having an average particle diameter of 1-10 xcexcm with a maximum particle diameter being 5 times as large as the average particle diameter or less and being represented by the chemical formula discussed below as a main component. The piezoelectric portion contains 0.05 to 10.0 mass % of NiO2.
An electrode is electrically connected to said the piezoelectric portion, and the piezoelectric portion is solidly attached to the ceramic substrate directly or via the electrode.
The piezoelectric ceramic compositions represented by the following general formula: Pb3(Mgy/3Nb2/3)aTibZrcO3.
In the above general chemical formula the following are satisfied: 0.95xe2x89xa6xxe2x89xa61.05; 0.8xe2x89xa6yxe2x89xa61.0; a, b and c are decimals falling in a range surrounded by (a,b,c)=(0.550, 0.425, 0.025), (0.550, 0.325, 0.125), (0375, 0.325, 0.300), (0.100, 0.425, 0.475), (0.100, 0.475, 0.425) arid (0.375, 0.425, 0.200) in the coordinates with coordinate axes of said a, b and c, and axe2x88x92b+c=1.00.
According to the present invention, there is further provided a piezoelectric element including a ceramic substrate, and a plurality of piezoelectric portions made of a piezoelectric ceramic composition containing a PbMg1/3Nb3/3O3xe2x80x94PbZrO3xe2x80x94PbTiO3 ternary system solid solution composition represented by the chemical formula discussed below as a main component. The plurality of piezoelectric portions 0.05 to 10.0 mass % of NiO, and include a plurality of electrodes thereon.
The plurality of piezoelectric portions are laminated with interposing negative electrodes and positive electrodes of the plurality of electrodes alternately in each gap between the piezoelectric portions provided in stories and a lowermost piezoelectric portion is solidly attached to the ceramic substrate directly or via said electrode.
The piezoelectric ceramic composition is represented by the following general formula: Pbx(Mgy/3Nb2/3)aTibZrcO3.
In the above general chemical formula the following are satisfied 0.95xe2x89xa6xxe2x89xa61.05; 0.8xe2x89xa6yxe2x89xa61.0; a, b and c are decimals falling in a range surrounded by (a,b,c)=(0.550, 0.425. 0.025), (0.550, 0.325, 0.125), (0.375. 0.325, 0.300), (0.100, 0.425, 0.475), (0.100, 0.475, 0.425) and (0.375, 0.425, 0.200), in the coordinates with coordinate axes of said a, b and c, and a+b+c=1.00.
Incidentally, in a piezoelectric element of this lamination structure, it is preferable that a ternary system solid solution composition has an average particle diameter of 1-10 xcexcm with the maximum particle diameter being 5 times as large as the average particle diameter or less.
According to the present invention, there is still further provided a piezoelectric element including a ceramic substrate, and a piezoelectric portion made of a piezoelectric ceramic composition containing a PbMg1/3Nb2/3O3xe2x80x94PbZrO3xe2x80x94PbTiO3 ternary system solid solution composition represented by the chemical formula discussed below as a main component. The plurality of piezoelectric portions contain 0.05 to 10.0 mass % of NiO, and said piezoelectric ceramic composition contains particles having NiO as a main component on the surface and/or in the interior thereof.
An electrode is electrically connected to the piezoelectric portion, and said piezoelectric portion is solidly attached to the ceramic substrate directly or via the electrode.
The piezoelectric ceramic composition is represented by the following general formula: Pbx(Mgy/3Nb2/3)aTibZrcO3.
In the above general chemical formula the following are satisfied: 0.95xe2x89xa6xxe2x89xa61.05: 0.8xe2x89xa6yxe2x89xa61.0; a, b and c are decimals falling in a range surrounded by (a,b,c)=(0.550, 0.425, 0.025), (0.550. 0.325, 0.125), (0375, 0.325, 0.300), (0.100, 0.425. 0.475), (0.100, 0.475, 0.425) and (0.375, 0.425, 0.200), in the coordinates with coordinate axes of said a, b and c, and a+b+c=1.00.
Also, in a piezoelectric element where the NiO particles are present, it is preferable that a ternary system solid solution composition has an average particle diameter of 1-10 xcexcm with the maximum particle diameter being 5 times as large as the average particle diameter or less. In addition, a particle having NiO as the main component may include only NiO or NiO with MgO solid solution.
In any of piezoelectric elements of the present invention, it is preferable that Ni is dispersed in the piezoelectric ceramic composition in such a concentration gradient that the concentration of Ni becomes higher from the interface between the piezoelectric portion and the substrate towards the thickness direction of the piezoelectric portion.
Pb in the piezoelectric ceramic composition may be replaced by at least one kind of element selected from the group consisting of Sr, Ca and Ba, by 2 to 10 mole %. Pb in the piezoelectric ceramic composition may also be replaced by La by 0.2 to 1.0 mole %.
It is preferable that the substrate has a thickness of 3 xcexcm to 1 mm, that the piezoelectric portion has a thickness of 1 to 300 xcexcm, that the ratio of the thickness of the substrate to the thickness of the piezoelectric portion (the thickness of the substrate/the thickness of the piezoelectric portion) is 0.1 to 30, and that a cross-section of the substrate in the thickness direction has a W-like shape having three inflection points.
According to the present invention, there is provided a method for producing a piezoelectric element including the steps of superposing a piezoelectric material containing a PbMg1/3Nb2/3O3xe2x80x94PbZrO3xe2x80x94PbTiO3 ternary system solid solution composition represented by the chemical formula discussed below as a main component the piezoelectric material contains 0.05 to 10.0 mass % of NiO on a ceramic substrate or on an electrode formed on the ceramic substrate, and subjecting the superposed piezoelectric material to a thermal treatment in an atmosphere whew 0.03-0.5 mg/cm3 (NiO conversion amount per unit volume of a space in a container) of atmosphere-controlling material having the same composition as the piezoelectric material is coexisted.
The piezoelectric material composition is represented by the following general formula: Pbx(Mgy/3Nb2/3)aTibZrcO3.
In the above general chemical formula the following are satisfied: 0.95xe2x89xa6xxe2x89xa61.05; 0.8xe2x89xa6yxe2x89xa61.0; a, band c are decimals falling in a range surrounded by (a,b,c)=(0.550, 0.425, 0.025), (0.550, 0.325, 0.125), (0.375, 0.325, 0.300), (0.100, 0.425, 0.475), (0.100, 0.475, 0.425) and (0.375, 0.425, 0.200), in the coordinates with coordinate axes of said a, b and c, and a+b+c 1.00.
A method for producing a piezoelectric element includes the steps of; superposing a piezoelectric material containing a PbMg1/3Nb2/3O3xe2x80x94PbZrO3xe2x80x94PbTiO3 ternary system solid solution composition represented by the following chemical formula discussed below as a main component, the piezoelectric material contains 0.05 to 10.0 mass % of NiO on a ceramic substrate or on an electrode formed on the ceramic substrate, and subjecting the superposed piezoelectric material to a thermal treatment in an atmosphere; wherein 0.03-0.5 mg/cm3 (NiO conversion amount per unit volume of a space in a container) of a atmosphere-controlling material having the same composition as the piezoelectric material is coexisted as a container for housing said electrode on which the piezoelectric material is superposed and a setter for mounting the piezoelectric material thereon.
The piezoelectric material composition is represented by the following general formula: PbM(Mgy/3Nb2/3)aTibZrcO3.
In the above general chemical formula the following are satisfied; 0.95xe2x89xa6xxe2x89xa61.05; 0.8xe2x89xa6yxe2x89xa61.0; a, b and c are decimals falling in a range surrounded by (a,b,c)=(0.550, 0.425, 0.025), (0.550, 0.325, 0.125), (0.375, 0.325, 0300), (0.100. 0.425, 0.475), (0.100, 0.475, 0.425) and (0.375, 0.425, 0.200), in the coordinates with coordinate axes of said a, b and c, and a+b+c=1.00.
The piezoelectric element according to the present invention can be used for condensers or various sensors, as a dense and small dielectric element or pyroelectric element.